The present invention relates to the preparation of aluminum alloys possessing an unusually advantageous combination of properties, particularly with regard to high strength, which is well retained at elevated temperatures as compared to known non-heat-treatable alloys, excellent formability, and favorable weldability characteristics, especially adapted for improved electric resistance welding of parts formed of wrought sheet. These alloys, being readily convertible to rolled sheets or plates displaying excellent formability, are particularly adapted for the production of body parts for transport vehicles including cars, trucks, barges, tanks and like articles.
Two physical properties of aluminum are especially important in the practice of resistance spot welding, the electrical resistivity, which is known to be low by comparison with well-known steels and therefore necessitates high welding currents for proper welds, and the contact resistance at the metal surface, which causes pick-up or sticking of the metal to the welding electrodes and undue variations in the size, shape and strength of the resulting weld when the values vary and are too high.
In view of improving the efficiency of energy consumption, it has become more urgent to accomplish reductions in the weight of motor vehicle parts. As a result, aluminum sheet alloys, which have been used extensively in the aircraft industry, as well as alloys of more moderate strength and greater formability, are of interest because of their reduced weight, good corrosion resistance, and other favorable properties. An important factor, however, in the consideration of aluminum is the question of its adaptability to the resistance welding techniques presently useful with the steels currently employed. Thus, the ease of resistance welding in terms of minimal control and lower current requirements comprises an important factor which makes it desirable to provide aluminum alloys exhibiting improved resistance weldability. Thus, a minimal requirement for a suitable aluminum alloy is that it should display increased electrical resistivity, as a reduction in total current requirements would render less critical the problems associated with contact resistance.
It has therefore been a principal object of this invention to provide aluminum base alloys characterized by a favorable combination of strength properties, which are well retained at elevated temperatures, useful formability, and excellent weldability, especially by resistance welding.
A further object has been to provide aluminum base alloys wherein the electrical resistivity has been substantially increased as compared to aluminum and its previously known commercial alloys, without impairment of strength, ductility and formability properties.
Another object has been the formulation of non-heat-treatable aluminum base alloy compositions, and procedures for producing them in wrought form, having improved electrical resistivity and capable of withstanding elevated temperatures without undue loss of strength and formability properties.
Further objects and advantages of the present invention will be apparent from the following description.